A few bones were giants. After being encased in plaster for shipment on a flatbed truck to the Denver Museum of Nature and Center in July, the tusks and skull of a Columbia mammoth weighed almost precisely 10,000 pounds.
“These things are treasures,” says Kirk Johnson, the museum’s chief curator. He called the lake at Snowmass “arguably the best high-elevation Ice Age site in the world.”
Johnson and other scientists have identified bones from at least 40 animal species, many of them mundane, such as mice and rabbits, but of number of them – like the mammoth, an elephant-like creature that stood 14 feet tall at the shoulders – now extinct for thousands of years.
But the bones, as exciting as they are, may prove to be secondary to the seeming minutia of seeds, pollen and insects, as well as the chemical composition of the lake bed itself. These tiny bits of evidence they hope will yield answers to one of the civilization’s most pressing questions: How are we changing our current climate?
By better understanding the natural climate changes of the Earth’s last interglacial period, scientists can better pinpoint what is unnaturally occurring as the result of human-caused emissions of greenhouse gases and modification of vegetative patterns.
“It’s not the Snowmass record in isolation,” said Johnson, referring to the improved paleo-climate reconstruction now underway. Rather, he explained, the evidence from Snowmass will be combined with studies of sediments from Idaho’s Bear Lake and from a volcanic cauldron in Mexico, along with ice cores in Greenland and Antarctica, to create a more robust understanding of the past.
Snowmass offers something exceptional, however: a high elevation, nearly 9,000 feet above sea level. As such, it can fill in gaps in existing climate-change sequences, but also provide clues about how places with higher elevations in the West may be impacted by rising temperatures.
“You feel climate change a little more intensively at higher elevations,” said Ian Miller, a paleontologist at the museum. And, he added, there just aren’t any comparable high-elevation sites around the world.
THE LAST WARM PERIOD
Scientists think the lake at Snowmass was created by a glacial episode called Bull Lake that ended quickly about 150,000 years ago. There have been about 10 glacial episodes in the last three million years.
The glacier that had scraped out the valley of Snowmass Creek deposited a ridge of rocks and detritus to the side, what is called a lateral moraine. Because of an unusual melting of ice, the lake was created on the ridge, a rare phenomenon.
In this last glacial interlude – we have had one major advance of glaciers since then – the climate was generally warm even than it is today, at least in Colorado. Even so, the climate fluctuated.
Scientists hope that they can get a sharper picture of those temperature and precipitation shifts during the last 80,000-year period of warmth, which was sandwiched by two ice ages. The point is to help create a better yardstick by which current times may be measured.
Other such climatic yardsticks exist. Ice cores from Antarctica go back 800,000 years. Those from Greenland go back only 110,000 years but provide far richer details, through evidence called proxies, about temperatures, precipitation and other aspects of climate. These cores have even recorded the arrival of the Romans in the British Isles, as evidenced by the increase in lead. The Romans introduced smelting.
The Snowmass site may sharpen this picture of the past even more. “It’s kind of a missing piece of the puzzle,” says Johnson.
While the Earth emerged from ice ages rapidly, lurching into warm weather in as little as 100 years, the glaciers expand more slowly. That’s what happened beginning 100,000 to 75,000 years ago, until glaciers once again gripped the high mountains of Colorado by about 50,000 years ago.
In this warm, interglacial period, Colorado was populated by a great many of species now extinct. There were the giant mammoths, with teeth adapted to grazing on grass, a giant bison half-again as big as today’s bison, with horns stretching 6 feet, 4 inches. Resembling the water buffalo of Asia, it made today’s bison look almost petite.
Also found at Snowmass was the claw of a Jefferson ground sloth. Like all the other creatures found at Snowmass, it was a herbivore, if not necessarily one you’d wish to encounter. It was the size of a grizzly bear. The claw, which is now displayed in Denver, looks lethal.
This is the highest elevation on earth at which the ancient Jefferson ground sloth – named after our nation’s third president, who studied paleontology – have been found.
Also found were a camel, which, surprisingly is the most frequent species found in Colorado, plus bones of a mule deer. The find may help scientists understand the evolution of mule deer in Colorado. And there was a horse – which became extinct in North America, “Probably because we ate it,” said Miller.
A MASTODON GRAVEYARD
But more than any other, the Snowmass site has yielded bones of mastodons, which were somewhat smaller than the mammoths, although still 10 feet at the shoulder, and somewhat bulkier, like, say, a football linebacker. Nearly four-fifths of all the bones belong to mastodon, however, which had the sharp teeth needed for browsing on the fibrous branches.
“We think it’s one of the finest mastodon sites in the world,” said Miller.
Scientists aren’t sure why the lake at Snowmass had so many mastodons; one hypothesis is that earthquakes played a role, and that a slumping hillside may explain the mass grave. More possible explanations may emerge as scientists examine the dozens of tusks.
“The amazing thing about tusks is that they grow every single day of the animals’ life,” explained Miller, at a presentation last week in Steamboat Springs. The tusks, he said, are like tree rings, which record annual growth, but more detailed yet, revealing new growth every two weeks. If the mastodon was a female, it will record when she had calves. The tusk rings also show seasonal fluctuations. As such, the scientists will be able to tell within two weeks within the season of the animal’s death.
Trees will also be able to tell stories. Logs were deposited along the ancient lakeshore, still fresh enough that they could be cut by chain saws. Miller said scientists hope to create a chronology spanning 1,000 years from study of the rings – amazing, when you consider that the longest tree ring sets in the American Southwest go back only 2,000 years.
Those tree rings will be able to tell stories of drought, of fires and their intensity, and also something about past beetle epidemics.
Conspicuously absent at the site are any bones of predators. This is in contrast with the La Brea Tar Pits of Los Angeles, where 80 percent of bones were those of predators. “That is one of the central questions we are trying to figure out,” said Miller at his presentation last week.
The discovery will be chronicled in the pages of National Geographic next March and in an accompanying film produced by Nova. National Geographic donated $50,000 to the research.
But the broader story of the Snowmass has yet to be sorted out, said Miller, who estimates it will take at least five years to decipher the meanings of the both the animals and the climate-change proxies. Even six months from now, he said, some new understandings will have been gleaned.
The bones might have remained entombed if not for worries about extended drought in the American Southwest.
The ancient lake was filled with sediment when modern settlers arrived, leaving a slightly-tilted meadow. In the early 1970s, the owner of the property, the Ziegler family, decided to scrape out the meadow to create a shallow lake for purely aesthetic purposes. The lake is about 600 yards from the bottom of the ski lifts.
After the drought of 2002, the Snowmass Water and Sanitation District began worrying about the firmness of its water supplies. It has sufficient water in wet years, but feels vulnerable to more senior water-right owners in the case of extended drought. After studying many climate models, the U.S. Bureau of Reclamation this year concluded that a 9 percent decrease in water volume in the Colorado River Basin may result in coming decades as the result of human-caused climate change.
With a cost estimated at $10.5 million, the water district purchased the reservoir site and ordered excavation to a maximum depth of 25 feet.
LIKE A TUPPERWARE LID
The initial discovery came Oct. 14. Jesse Steele, a third-generation heavy equipment operator, noticed a bone. Bones of cattle, even the modern bison, aren’t all that uncommon. This one was. It was from a juvenile mammoth.
Working through the state archaeological office, the water district had by early November entered into a partnership with the Denver museum, the nation’s fourth largest nature museum, to take responsibility for the excavation and curating.
Gleefully, Johnson, Miller and other staff and volunteers plunged into the dig, amazed at the proliferation of bones, tusks and 40-foot-long logs.
Key to the uncommon preservation were layers of silt, peat and clay, all of them barriers to oxygen. Oxygen degrades organic matter rapidly. Instead, some of the 49 mastodon tusks were still white. Leaves were still flexible and stayed green as long as five minutes. Beetle carcasses were iridescent, changing color depending upon the angle of their observation.
“This clay had the clay equivalent of a Tupperware lid,” said Johnson. “In this case, we got lucky.”
Fringed by green aspen trees, the perimeter of the lake bed is deep red, a dominant color of the Elk Range in which Snowmass is located. Below were the varying layers of muck, dark in color. Here and there peat could be broken up to reveal the grasses, leaves and the occasional beetle.
When scraped by earth-movers, the freshly exposed clay looks and feels like modeling clay, or perhaps the Play-Doh sold at toy stores. Where it had been exposed to the sun, though, it was wrinkly, cracking in wide fissures.
Collaboration between the museum and water district was smooth. Paleontological excavation lasted for just a few weeks until snow stopped the digging last fall, then returned in May for another 50 days of digging. Supervised by the museum’s six paleontologists, staff and 240 volunteers moved 8,000 pounds of mud shovel by shovel full, heavy equipment often assisted the paleontologists.
The museum was careful not to delay reservoir completion. “Otherwise nobody is going to call us when something like this happens,” said Miller. “We are very careful about this.”
There was never any doubt about assistance, said Kit Hamby, manager of the water district. “It’s pretty rare to have something like this dropped in your lap, and we wanted to make the most of it,” he explained.
In early July, soon after the formal excavation had ended, Hamby was standing in the pit, explaining the excitement of being involved in a world-noteworthy paleontological dig, Hamby paused mid-sentence. He thrust his right arm out, his hand balled into a fist, the construction-site signal to stop immediately.
“It looks like a bone,” he yelled to the operator of the excavator below. The operator hopped out, filched the 18-inch bone from the mud, and tossed it up to Hamby.
For now, museum volunteers and staff are busily preparing the bones for long-term preservation. The key is slowly drying the bones. Dry them out too rapidly and they will crack, explained Johnson. Leave them too moist and they will mold.
The several dozen scientists who gathered from around the world at Snowmass have started puzzling over their findings, to better understand the past and how that may educate our decisions about the future.
Hamby hopes that the digging isn’t entirely over. He can envision a sequence in which paleontologists return every five years or so with new funding, new insights, and new questions that the remaining treasures may help answer. It could help science, he says, but also the summer economy of Snowmass Village.